Although various methods of stereoscopic viewing are employed, in recent years, the most common such method has been parallax viewing, which involves showing left-view and right-view images to a viewer so as to create the illusion of stereoscopy through inter-image parallax.
In this form of stereoscopic playback, the depth perceived by the viewer is dependent on the magnitude of the parallax separating the left and right images. As such, the viewer's eyes perform focus adjustment in order to perceive the left and right images stereoscopically.
The angle between the direction of the left eye when viewing a 2D display and the direction of the left eye when viewing a 3D display is termed the parallax angle. The greater the sudden change of parallax angle, the more likely ocular fatigue becomes, as the eye must suddenly change direction to perceive the new angle. Although the parallax angle is defined with respect to the left eye, the same parallax angle is generally also definable with respect to the right eye. The greater the change in parallax angle, the more the eye must move in response to the change. The need to move a greater distance over a short time is a cause of ocular fatigue.
The below-cited publications describe publicly-known inventions of technology for reducing ocular fatigue when viewing 3D video.
The playback device described by Patent Literature 1 does not immediately begin 3D playback upon input of left-view and right-view signals, but instead waits for a predetermined interval to pass before doing so. When performing a switch from 2D to 3D, the playback device reduces ocular fatigue by gradually changing the parallax. The gradual change is one of a monotonic increase, a concave change, or a convex change (see FIG. 4 and paragraph 0015 of Patent Literature 1). During this gradual change, a target parallax is calculated by the parallax calculating means 12 and used, as determined, by the parallax determining means 14 (see paragraph 0008 of Patent Literature 1).